1. The Field of the Invention
The invention relates to a core glass in the alkali-zinc-silicate glass system for a fiber-optic light guide and a fiber-optic light guide made from this core glass.
2. The Related Prior Art
Fiber-optic light guides are increasingly widely used for light transmission in the most different engineering and medicinal fields, e.g. in general industrial engineering, in lighting and traffic engineering, in the automobile industry, in dentistry, in endoscopy, etc. Fiber-optic light guides, which comprise individual fibers assembled into a fiber bundle, are usually made from glass because of its good thermal and chemical resistance. The individual light fibers guide the light by total reflection. The most widely used light guide fibers are the step index fibers, which comprise a core made from a core glass, which has a constant index of refraction over its cross-section. The core glass is surrounded by a cladding made of cladding glass, which has a lower index of refraction than the core glass. The total reflection occurs at the boundary surface between the core glass and the cladding glass.
The amount of light, which can be coupled into this sort of fiber, is proportional to the square of the numerical aperture (NA) of the fiber and the cross-sectional area of the core fiber.
The attenuation of the light in the fiber also plays a great role as well as the numerical aperture. Thus only a glass that has a low attenuation of light can be used as a core glass. Because of the high purity requirements the raw materials for the glass melt of this sort of core glass are very expensive, which can lead to a high cost for this sort of optical fiber and thus the manufactured light guide. Furthermore toxic ingredients, such as PbO, CdO, BeO, Tl2O, and ThO2, can no longer be used because of environmental considerations.
Besides the light flux, which the fiber-optic light guide transmits, frequently poor transmission of color shades of the light by the light guide plays a significant role. Because of the spectral transmission dependence of the core glass, which the fiber contains, a more or less strong shift in the color location of the coupled light source occurs, which is made most notable by a yellowish tinge or tint of the light issuing from the light guide. This causes trouble in applications that require a color neutral reproduction, e.g. in medicinal endoscopy, in photographic image documentation to differentiate between healthy and malignant tissue.
The reliability of the fiber, especially in mobile applications, i.e. which depends on its resistance to aging due to stress caused by temperature changes between about −50° C. and 110° C., its resistance to mechanical stresses, especially resistance to vibration and chemical resistance to environmental influences, is of importance. Especially the hydrolytic resistance and the acid resistance of the core glass are of importance. The density of the fibers is also of importance, since it has a direct influence on the fuel consumption and load on the aircraft or automobile including the fibers. The density of the step index fiber is primarily determined by the density of the core glass.